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Title: Late Devensian ice sheet dynamics and the deglaciation of the Hebridean shelf, western Scotland, UK
Author: Arosio, Riccardo
ISNI:       0000 0004 6498 1530
Awarding Body: University of Aberdeen
Current Institution: University of the Highlands and Islands
Date of Award: 2017
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The reconstruction of marine-based paleo ice sheet dynamics can reveal long-term ice sheet activity, and in turn provide constraints on the response of modern marine ice sheets (e.g. the West Antarctica Ice Sheet) to climate change. The marine-terminating Hebrides Ice Stream (HIS) flowed across the western Scottish shelf during the last glacial maximum (3024 ka) and drained a large portion of the northern sector of the British Irish-Ice Sheet (BIIS), affecting its stability. This thesis aims to examine how the HIS evolved and interacted with the changing climate and the underlying landscape after 27 ka. The work is subdivided into: a) an investigation of modern high-resolution bathymetry data coupled with seismic data with the aim of reconstructing deglacial dynamics; b) the analysis of Pb isotopic composition in sediment cores on the shelf in order to locate glacial sediment provenance; c) a study of Hebrides shelf core sedimentology and microfaunal assemblage to reconstruct Lateglacial paleoenvironmental changes. A three-stage deglacial pattern, where topography played a critical role, is defined: i) ice stream margin retreat punctuated by standstills, ii) topography-controlled fjordic retreat, with evolution from a coherent ice-sheet to separate fjord tidewater glaciers, and iii) a stabilisation at the transition from tidewater to land-based ice margins. Between 21 and 15 ka, fine-grained sediments transported by meltwater plumes were the product of erosion of Neoproterozoic basement, while the coarse-grained sediments were instead sourced from island igneous rocks. These results indicate prevailing sediment input from NW Scotland. Lateglacial sediment deposition was strongly influenced by shelf currents and shows wide variation. Therefore, the seismic and sedimentological interpretations need to be considered only on a local scale. Glacimarine sandy deposits in the Muck Deep region support a prolonged glacial occupancy until the latest stages of GS-1 (12.8-11.7 ka), and are at odds with recent studies indicating earlier glacial retreat. The thesis demonstrates the complex interactions between BIIS evolution, subglacial landscape and ocean dynamics. The outcome of this research can be useful to inform future numerical reconstructions.
Supervisor: Howe, John ; Crocket, K. C. ; O'Cofaigh, Colm ; Dove, Dayton Sponsor: Seventh Framework Programme (European Commission)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ice sheets ; Sedimentology ; Submarine topography ; Periglacial processes